Doctors who treated him at the University of Virginia hospital in 2000 believe that the man's powerful sex addiction was caused by an egg-sized tumor in his brain.

"It turned out he was a guy who had made it into his 40s without having any problem with this," said Dr. Russell Swerdlow, a UVa associate professor of neurology. "He had a brain tumor that was damaging the part of the brain that controls impulse."

Once the tumor was removed, the man's sexual obsession disappeared. Swerdlow believes this is the first known case to link damage of the frontal lobe with pedophilia.

Swerdlow and Dr. Jeffrey Burns, a former UVa physician, have written an article on the case. It was published in the March edition of Archives of Neurology.

"The most interesting part of this is getting into the hardwiring of morality and free will," Swerdlow said. "It raises the question, how free is free will?"

This philosophical question is being investigated by doctors across the country. And the answers they find through their research could have serious implications - not just for individual treatment but for the criminal justice system as well.

Brain scans conducted on murderers, for example, show that there is sometimes damage or poor function of the prefrontal cortex, a part of the brain that lies just behind the forehead and eyes.

Such scans and other scientific studies of the mind may one day be widely used in courts as evidence for the defense, as it was for Swerdlow's patient.

"This guy was going to go to prison and what he needed was an operation, not incarceration," Swerdlow said.

Dr. Burns first met the man after he showed up at UVa hospital complaining of headaches and saying he feared he would rape his landlady.

Burns described his behavior as impulsive and hypersexual.

"He was propositioning the nurses and the female residents," Burns recalled. "He had no concern that he urinated on himself or how he was perceived by other people. He would stop the conversation between the doctor and himself and ask women to get into bed with him."

Neurological exams showed the man was unable to write or copy drawings normally. An MRI was ordered.

"We found a very large brain tumor replacing the entire orbitofrontal lobe," Swerdlow said.

Swerdlow said the man was relieved that the tumor provided an explanation for his sociopathic behavior.

"He's grateful that he was properly diagnosed and properly treated," Swerdlow said. "He's relieved to know that he isn't the 'evil' person that he thought he was destined to be."

According to Swerdlow's paper on the case, the man secretly visited child pornography Web sites and solicited prostitutes during 2000. The patient said that he had never participated in these activities before.

"It started with a fascination of pornography, including child pornography, and as the tumor grew the symptoms worsened," Swerdlow said.

When the man's wife found out he had made subtle sexual advances toward a young girl, she kicked him out of the house. He was found guilty of child molestation and medicated with drugs intended to produce chemical castration.

A judge ruled that he had to pass a 12-step sexual addiction program or go to jail. But the man was thrown out of the class after he solicited sexual favors from staff and classmates.

Coincidentally, he showed up at UVa's emergency room the night before his sentencing.

"There was some concern he was malingering in an effort to avoid his court date," Burns recalled.

But then the tumor was found. It was located in the right lobe of his orbitofrontal cortex, which is known to be tied to judgment, impulse control and social behavior.

"The brain tumor was resected and the symptoms were resolved," Swerdlow said. "He was given a second chance at a program for sex offenders. He successfully completed the program."

But seven months after the tumor was removed, the headaches began anew. And the man again started viewing porn.

An MRI revealed tumor regrowth. In 2002, a tumor was removed for the second time. And for the second time, the behavior disappeared.

"He's doing great, but there is always the possibility that it could grow back," Swerdlow said. "It's a really bizarre, Kafkaesque situation."

Swerdlow argues that the case legitimizes the question of whether some sociopathic behavior is caused by brain disorders.

"Will we one day find that people perform criminal acts because they have some kind of damage or abnormality to this part of the brain?" Swerdlow asked. "I think that we are just beginning to scratch the surface of how personality is hardwired."

"Researchers are investigating whether there are certain groups of people born this way," he said. "Maybe that part of their brain has developed differently. Maybe that's just the way they came wired from the store."

George Thomas, a UVa professor emeritus of philosophy, said this idea goes back at least to the 1920s.

"A lawyer named Clarence Darrow argued that all criminal behavior was caused by mental or physical illness," Thomas said. "He said we should think of criminal behavior as a disease that could be treated mentally or physically."

Thomas said if the man truly was unable to control his actions, he should not be held morally responsible for them.

"If the conditions that produce the behavior are independent of that person's values, you shouldn't hold that person accountable," Thomas argued. "You should try to treat the condition."

An example of this would be someone with Tourette syndrome who shouts out obscenities.

The problem is that it's often difficult - if not impossible - to judge whether a person is unable to suppress their impulses.

"You certainly can't generalize from this one case to say that all pedophiles can't control their behavior," Thomas said.

And Thomas isn't convinced that Swerdlow's patient is entirely guilt-free.

"The tumor wasn't completely the cause of the behavior," Thomas said. "He had to have the impulse somewhere within him. The tumor simply made it difficult for him to act against that impulse."

"Sexual impulses are common to everyone, of course," he said, "but I don't believe the impulse to molest children is common in everyone."

Swerdlow emphasized that he is not suggesting that every pedophile has a brain tumor and should escape incarceration.

"The difference in this case was that the patient had a normal history until he developed the tumor," Swerdlow said. "Most pedophiles develop problems early in life."

It's known that deviant behavior can be caused by several kinds of brain damage, including tumors, trauma and infections such as encephalitis. Swerdlow hypothesized that abnormalities could be caused on biochemical levels that scientists aren't even aware of.

"Studies suggest that when damage is done to the frontal lobe before 18 months, people never learn right from wrong," Swerdlow said. "When damage is done after that time, people can learn right from wrong but they can't control their impulses. There is no longer regard for long-term consequences, only short-term gratification."

"Nothing puts the brakes on their behavior. They are always in trouble," he said. "If their brain wants something, they take it."

Swerdlow said this was the case with his patient. The man knew his actions were wrong "but the pleasure principle overrode his restraint."

There are many documented cases of behavioral changes caused by damage to the frontal lobe. The most famous probably is that of railroad worker Phineas Gage.

In 1848, an explosion sent a railroad spike through the front of Gage's skull. He survived, but after the accident the once passive man was prone to rage.

Some of the most compelling modern visual evidence for the link between brain damage and violence is the work of Dr. Monte Buchsbaum, a professor of psychiatry and director of the neuroscience PET laboratory at Mount Sinai School of Medicine in New York. In 1997, Buchsbaum conducted the largest brain-imaging study of murderers ever.

Buchsbaum performed PET scans on 22 people on trial for murder and 22 other people of similar age who had no history of violence. The accused murderers, as a group, had lower glucose metabolism in the prefrontal cortex, showing diminished activity in brain areas which normally function to inhibit aggressive impulses.

"I think that people can become murderers as a result of brain damage, but they are not predestined to become murderers," Buchsbaum said. "There is not a murder center in the frontal lobe. These areas in the frontal lobe are involved in motivation, mood regulation and impulse control. And these personality features are applied across a wide range of behavioral scenarios."

Buchsbaum doubts that brain scans will ever be used as a technique to identify potential murderers or even less violent criminals.

"They will never find a brain center that makes people commit murder," he said. "The brain is just not wired that way."

Brain damage, Buchsbaum argues, can have a range of unpredictable effects. It could cause something as minor as antisocial behavior or something as severe as murder.

Scientists can provide information about the link between deviant behavior and brain damage. But ultimately, it will be up to the legal justice system and juries to make sense of new scientific discoveries and decide how accountable people are for their actions.

"The goal of the legal system is to cure criminal behavior. This is often done through incarceration," Swerdlow said. "Perhaps, in the future, there will be others ways to manage sociopathic behavior - maybe prescription drugs or operations."

He concluded: "We're dealing with the neurology of morality here."

Claudia Pinto, a staff writer for The (Charlottesville) Daily Progress, at (434) 978-7266 or cpinto@dailyprogress.com.